What are quantum dots? They're these tiny luminescent crystals that have all sorts of interesting, and useful properties. They're semiconductors, and their electronic characteristics change based on how big each crystal is. Since researchers can control to a high degree of specificity how big the crystals are, they can therefore control their electrical properties.

Basically, any time you're shining a light at something, quantum dots can be useful. Differently sized dots reflect and absorb different lights. They're a prime candidate for quantum computers, for photovoltaic devices, and for photodetectors. But one of the big areas where quantum dots are promising is in medicine.

Often, doctors or researchers want to dye something in the body to see what's going on - where the blood or cells are moving, or how much of something is in the body. Normally they use organic dyes, but those often get lost, wear out and aren't nearly specific enough. Quantum dots, however, can be bright (20 times brighter than the standard fluorescent dies), stable, and long lasting. But there's still one question: are they safe?

To find out, researchers turned to primates. We already knew they were safe in other lab animals, but that's not that useful, said coauthor Paras Prasad in the press release. "So far, such toxicity studies have focused only on mice and rats, but humans are very different from mice. More studies using animal models that are closer to humans are necessary,"he said. So, to get closer to humans, they injected four rhesus monkeys with quantum dots made of cadmium-selenite. The monkeys are totally fine for over 90 days after the injection. And, two years later, still no signs of illness. The research was published in Nature Nanotechnology.

Next comes the big test: people. The monkeys did have a build up of cadmium, although it didn't seem to effect them. It remains to be seen how humans will react.